Gravimetric Study Of A Retrogressive Landslide In Southern Italy

Post-failure activity of the December 1993 Senerchia slump-earthflow was characterised by intermittent recession of the headscarp and earthflow movements. The retrogression showed considerable spatial variability, depending on the properties of the geological materials. The retrogressive failures were preceded by intense fissuring of the ground in the crown zone. Two microgravimetric surveys were carried out in order to detect possible spatial-temporal density variations in an area upslope of the headscarp. Although it was not possible to recognise any significant temporal density changes, this surveying revealed the presence of a negative anomaly which coincided with the area of maximum headscarp retreat. The gravity modelling was constrained by borehole information and new headscarp exposures produced by a series of retrogressive failures suggested that the origin of the anomaly might be associated with a hollow in an underlying clay-rich bedrock which had been subsequently filled by coarse colluvium. A possible concentration of groundwater in the hollow and its discharge towards the headscarp area controlled the local slope instability. The results of this study showed that microgravimetric surveys conducted upslope of retrogressive landslides can provide useful information on subsurface lithological heterogeneities that may control the amount and preferential direction of upslope landslide enlargement.     

Distribution,Population Structure, ­Population Biomass and Morphological Characteristics of the Tunicate Pyura stoloniferain the Bay of Antofagasta,Chile

Abstract. The present study analyzes the distribution, population structure, population biomass and morphological characteristics of the intertidal tunicate Pyura stolonifera (Heller, 1878) in the Bay of Antofagasta, Chile, where the species shows a reduced geographical range extending around 60 – 70 km. Three sites along its distribution were studied. At the central site the tunicate presents the widest intertidal belts, reaching nearly 11 m (the mid‐intertidal‐Pyura‐zone shows the higher percent cover). Population dry biomass here averaged up to 20.45 kg·m^–2, representing one of the highest intertidal specific biomasses reported in the literature. Lower values occur towards the borders of its distribution. Population densities were over 1800 indiv.·m^–2 at mid‐intertidal‐Pyura‐belts. Crowding and competition potentially affect morphological characteristics and the energy/tissue allocation along the intertidal and geographical gradient of P. stolonifera.     

基于数学形态学的地震带图像识别分析

本文通过“滑动窗口”的方法将离散的地震点分布转化为反映其密度分布的灰度图像,再以数学形态学中骨架提取方法来提取地震带位置。首先对地震分布密度的灰度图像进行连通分析,认为主要的连通成分即对应了地震密集分布的地震带所处位置,之后对主要连通成分通过Fourier滤波来平滑图像内部及边缘的噪声,对经过Fourier滤波的图像运用数学形态学骨架提取方法来提取出骨架,以识别地震带的位置。本方法在使用模拟数据检验方法的有效性之后,应用于大华北地区的地震记录,对提取出的骨架采用GIS中的缓冲分析方法进行统计检验,同时结合地震专家划分的地震带进行比较,结果令人满意。     

河口海岸潮滩蟹类生物扰动行为过程研究进展

河口海岸潮滩是具有较高生物生产力和生物多样性的生态系统。蟹类作为一种典型的生态系统工程师,分布广泛、种类繁多,可影响整个潮滩生态系统的物质与能量循环。蟹类的分布与盐度、淹水时长、湿度、温度、底质等非生物因子有关,也与植被、捕食作用、种内种间竞争等生物因子和人类活动有关。蟹类挖掘洞穴,形成了优先排水通道,增加了土壤蒸发速率,改变了孔隙水循环以及土壤的物理化学性质,进而可影响潮滩泥沙稳定性以及微地貌形态,甚至会影响中长期潮滩地貌演变。目前,蟹类对于沉积物稳定性、泥沙输运规律、微地貌演变的影响依然有待深入研究,有必要开展中长期现场观测和试验、多因子驱动下系统演变数值模拟以及综合分析,推动相关研究从定性向定量层面迈进。     

贝类种群壳形态性状多态性研究进展

贝类壳形态具有丰富、复杂的多态性。壳形态作为贝类重要的数量性状是一种环境适应的进化,是不同生理功能适应其生活方式的结果,受环境和遗传因素影响,与贝类的生长、存活、代谢及繁殖等生态、生理行为密切相关。通过贝类可量可数性状建立的壳形态数值分类学方法已在贝类种群形态学比较及群体亲缘关系研究中广泛应用。本文对贝类种群壳形态性状的多态性研究进行了综述,并对壳形态分析方法在贝类种质资源评估（种群识别）及遗传育种（壳宽型/深凹型品系选育）中的应用提出展望,旨在为研究者较全面了解壳形态性状的多态性和分析方法提供参考。     

Numerical simulation of large wood deposition patterns and responses of bed morphology in a braided river using large wood dynamics model

This study discusses the reproducibility of a numerical model for simulating the morphodynamics involved in the transport of large pieces of wood in a braided river, considering the root wad effect and jam formation. The developed numerical model can simulate the behaviour of large pieces of wood using a two-dimensional depth-averaged Eulerian flow model that calculates the water flow and bed morphology. A Lagrange-type wood transport model is used herein, and the applicability of the combined model is discussed through a comparison with obtained experimental results. From the simulation results, we calculate the total braiding index and estimate the deposition patterns of wood pieces for comparison with the experimental results. We then analyse the bed morphology responses and wood deposition patterns in terms of the root wad effect and input supply. Moreover, we discuss the advantages and limitations of the proposed model to predict the large wood dynamics considering the bed morphology. © 2019 John Wiley & Sons, Ltd.     

The effect of accelerated soil erosion on hillslope morphology

Intensive agricultural land use can have detrimental effects on landscape properties, greatly accelerating soil erosion, with consequent fertility loss and reduced agricultural potential. To quantify the effects of such erosional processes on hillslope morphology and gain insight into the underlying dynamics, we use a twofold approach. First, a statistical analysis of topographical features is conducted, with a focus on slope and gradient distributions. The accelerated soil erosion is shown to be fingerprinted in the distribution tails, which provide a clear statistical signature of this human-induced land modification. Theoretical solutions are then derived for the hillslope morphology and the associated creep and runoff erosion fluxes, allowing us to distinguish between the main erosional mechanisms operating in disturbed and undisturbed areas. We focus our application on the landscape at the Calhoun Critical Zone Observatory in the US Southern Piedmont, where severe soil erosion followed intensive cotton cultivation, resulting in highly eroded and gullied hillslopes. The observed differences in hillslope morphologies in disturbed and undisturbed areas are shown to be related to the disruption of the natural balance between soil creep and runoff erosion. The relaxation time required for the disturbed hillslopes to reach a quasi-equilibrium condition is also investigated. © 2019 John Wiley & Sons, Ltd.     

Numerical simulation of sedimentation process in reservoirs and development of a non-coupled algorithm to improve long-term modeling

This paper investigates the validity of a quasi-steady approximation for sediment transport and presents a new algorithm based on this concept. The developed non-coupled algorithm interacts among hydrodynamic, sediment, and morphology modules which are based on depth-averaged Navier-Stokes equations for the flow, the three-dimensional equation of conservation of sediment, and the mass balance between the bed and sediment (Exner equation) to simulate the reservoir sedimentation process. The non-coupled algorithm solves both the short-term scale and the relatively long-term scale problems of reservoir sedimentation. The proposed algorithm is verified using field data and by comparison with other accurate algorithms. Based upon the results of this investigation, the developed algorithm can be used to simulate long-term reservoir sedimentation while considerably decreasing the computational costs and preserving computational accuracy. The computational cost of the non-coupled algorithm is about 97% less than the conventional semi-coupled approach whereas the errors (Root Mean Square Error, Average Relative Error, and Maximum Relative Error of bed level) of the developed algorithm are approximately 15% greater than those for the semi-coupled algorithm for the average value.     

腾格里沙漠东南缘横向沙丘粒度变化及其与坡面形态的关系

腾格里沙漠东南缘的横向沙丘因断面形态不同可分为凸形和凹形两种类型。横向沙丘丘顶至落沙坡为风沙堆积区, 沙粒沿滑落面作重力下滑时, 较粗颗粒先到坡脚, 背风坡的沉积物下粗上细。沙丘迎风坡则因断面形态不同而影响沙丘表面过程。其中, 凸形沙丘迎风坡为高饱和风沙流环境, 下部有大量蚀余粗颗粒, 上部发生加积, 故下粗上细; 而凹形沙丘的迎风坡则为低饱和风沙流环境, 表面普遍风蚀, 前积纹层出露表面, 沉积物下粗上细, 实际上是背风坡沉积物重力分异结果的重现。沙丘高度与平均粒径和分选参数之间具有良好的一致性。风成床面作为一种地形, 对风沙地貌表面过程产生了重要影响, 这是风沙地貌尚须努力开拓的领域之一。     

从水动力学角度探讨沟鞭藻孢囊形态对沉积环境的适应

摘 要　 从水动力学角度出发‚以孢囊沉降速率和孢囊强度两个概念为研究基点‚半定量化 地探讨了孢囊形态对沉积环境的趋同适应‚得出在低纬区的孢囊或远岸区的孢囊个体大、壁 薄、刺发育、长或多次分叉并结合成网络状;在高纬区或近岸区发育个体小、壁厚、刺不发 育的孢囊。